Parco naturale dei Mulini, Nature reserve in San Quirico d'Orcia, Italy.

Parco naturale dei Mulini is a protected natural area in Bagno Vignoni, in the municipality of San Quirico d'Orcia, province of Siena. It was one of the main milling centres in the Siena area, and its mills were fed year-round by thermal water. Old images of the spa show the springs, the bath buildings, the cisterns, the mills and the gorelli, small streams of thermal origin.

The mills formed one of the main milling centres in the territory of Siena, in the comune of San Quirico d'Orcia. They were abandoned in the 1950s after operating as one of the area's principal productive sites. In 1997 the site was designated a nature park.

The mills represent centuries of local craftsmanship relying on natural thermal resources to support community life. People depended on these structures for their daily bread, making them central to the rhythm of village existence.

The site can be explored through marked trails that lead to the underground structures and natural caves. Visitors can choose between self-guided exploration or joining organized tours to better understand the complex.

The mills tap directly into thermal water flowing from the rock, ensuring constant temperature and preventing freezing in winter when conventional mills shut down. This clever use of natural heat meant the complex could produce flour continuously throughout the year.